Enumerating stably trivial vector bundles with higher real $K$-theory

Abstract

This paper explores periodic phenomena in the group ${\mathrm{Vect}}_r^0({\mathbb{CP}}^{r+c})$ of stably trivial, complex rank $r$ topological vector bundles on ${\mathbb{CP}}^{r+c}$. For $1\le c<r$ and $c\le 2p-3$, we give a complete computation of the $p$-torsion in ${\mathrm{Vect}}_r^0({\mathbb{CP}}^{r+c})$, and we relate these $p$-torsion bundles to vector bundles on spheres. We also compute ${\mathrm{Vect}}_r^0({\mathbb{CP}}^{r+c})$ in full when $c=3$, extending computations of the second-named author when $c=1$ and $c=2$. Finally, for a fixed corank $c$ which is larger relative to the prime $p$, we show there are families of $p$-torsion in ${\mathrm{Vect}}_r^0({\mathbb{CP}}^{r+c})$ that are periodic in $r$ with period $p$. We detect these using Weiss calculus and certain higher real $K$-theory homology groups.

35 pages, comments welcome! Substantial revisions: exposition revised, corrections to computational errors, added discussion of geometry, and added complete corank 3 computation. Homotopy of unitary group results are now omitted (will appear as separate note)